The present invention relates generally to patient ventilation systems and, more particularly, to a motor blower assembly incorporating an improved brushless D.C. motor assembly of reduced size and which is configured to rotatably drive a precision impeller with minimal variations in an air gap between the rotating impeller and the blower housing such that the blower assembly operates with improved efficiency.
The impeller includes a plurality of vanes that are optimized to improve the flow capability of the blower assembly with a reduced amount of power consumption at the motor assembly. Advantageously, because of its small size, low weight and reduced output of noise, vibration and heat, the blower assembly is suitable for use in sensitive environments such as in a hospital room or bedroom of a respiratory care patient undergoing continuous positive airway pressure (CPAP) treatment.
Brushless D.C. motors are known to operate at a relatively high levels of efficiency under low-load conditions as compared to conventional (brushed) D.C. motors. Furthermore, brushless D.C. motors are known to generate a reduced amount of noise as compared to brushed D.C. motors. As such, brushless D.C. motors are well-suited for use in relatively small or miniaturized fans or blower assemblies such as may be used as for cooling purposes and/or for generating compressed air.
Examples of blower assemblies include that which is disclosed in U.S. Pat. No. 4,164,690 issued to Muller et al. which describes a compact miniature fan such as may be used for cooling electronic components. The miniature fan of the Muller reference includes a radial fan wheel disposed within a housing and which is mounted to a rotor of a motor assembly. The motor assembly is configured as a stator mounted on a base plate of the housing. The rotor is secured to an underside of the impeller and rotates about the motor shaft.
Although the miniature fan of the Muller reference is disclosed as having a relatively small size of about 23 mm in height and 73 mm in width, the miniature fan is not believed to be suitable for certain applications such as in a CPAP device which requires an even smaller size and lower-weight blower assembly. Furthermore, the configuration of the radial fan wheel as used in the Muller reference is not understood to possess the ability to produce the required compressive flow at a high efficiency level. Furthermore, the miniature fan as used in the Muller reference is not understood to operate at a reduced noise level and with reduced vibration output as is required in a portable CPAP device.
U.S. Pat. No. 6,551,074 issued to Kudo et al. discloses a centrifugal fan having an electric motor and an impeller mounted on the electric motor. The centrifugal fan draws air into one side of a housing of the fan and discharges the air out of the housing in a radial direction. The electric motor includes a stator which has a stator-side magnetic pole and a rotor which rotates about the stator. The impeller includes a plurality of blades which draw air into the axial side of the fan.
Unfortunately, the blades in the fan of the Kudo reference form a relatively large air gap with the housing such that, during operation, the fan is believed to generate fluid eddies as a result of air flowing between the air gap. The fluid eddies are believed to interfere with the aerodynamic efficiency of the compressed air flowing through the vanes toward the outlet. In addition, the reduced aerodynamic efficiency of the fan is believed to result in a concomitant increase in noise such that the Kudo device is also not believed to be suitable for use in a portable CPAP device.
As can be seen, there exists a need in the art for a miniaturized blower assembly incorporating a brushless D.C. motor capable of operating at high efficiency in compressing air and which has a reduced noise, vibration and heat output during its operation such that the blower assembly is mountable upon or adjacent to a patient such as in a portable or wearable CPAP device. More specifically, there exists a need in the art for a blower assembly wherein the impeller is capable of rotating in close proximity to a housing of the blower assembly in order to minimize the formation of fluid eddies which could otherwise compromise the compressive efficiency of the blower assembly and which may contribute to the generation of excessive noise and vibration by the blower assembly.
Furthermore, there exists a need in the art for a blower assembly which is mountable in such a manner as to minimize the outwardly-directed radiation of structure-borne vibration as sound. Additionally, there exists a need in the art for a blower assembly that is mountable in such a manner as to attenuate or reduce the transmission of vibration to a patient undergoing respiratory treatment such as CPAP therapy. Finally, there exists a need in the art for an economical process for producing a blower assembly with relatively small tolerances in order to provide the desirable qualities of high operating efficiency and reduced noise and vibration output.